An epidemiologic study of chronic obstructive lung disease (C.O.L.D.) is being done in the population of Tecumseh, Michigan. It consists of a longitudinal study of morbidity and mortality in persons examined in 1962-65. Follow-up and re-examination of the cohort was carried out between January, 1978 and June, 1979. The principle objective of the study is to relate findings at the initial examination (risk factors) to subsequent illness, decline in lung function, and death. End points include chronic bronchitis, asthma, emphysema, other C.O.L.D., excessive decline in lung function and death from chronic lung disease and other causes. Risk factors include selected personal, demographic, physiologic, genetic and familial characteristics such as smoking and drinking habits, socio-economic status, experience of respiratory infections and allergic conditions, level of lung function, blood and serum protein type, skin sensitivity to allergens and immunoglobulin levels. The predictive ability of risk factors acting singly and in combination, will be assessed for each end point. Particular attention will be given to interaction between smoking and other relevant factors. Additional objectives include improvement in diagnostic accuracy of different types of C.O.L.D. in epidemiologic studies, and identification of lung function tests which are most suitable for prediction and early detection of C.O.L.D. in the general population.